1. Field of the Invention
This invention relates to the fabrication of a sealed and shielded hydraulic pump assembly for use in a system such as an anti-lock braking system on an automobile. Hydraulic valves or actuators are controlled by an electronic control unit which applies electric current to solenoid coils surrounding the valves to actuate the valves. The assembly is sealed and a seal is established between a hydraulic subassembly and the electronic control subassembly.
2. Description of the Prior Art
The hydraulic unit for anti-lock braking systems on automobiles includes a hydraulic pump and an electrical control unit. The hydraulic pump or valve actuator unit of these devices includes a number of valves or domes in the form of cylindrical members or fingers. The valve element in these cylindrical members is actuated by the magnetic force induced by the current flowing in a toroidal solenoid coil in which the cylindrical member fits. Standard units can have six to ten valve actuators.
Commercially available systems employ an assembly consisting of two separate components. A hydraulic control unit containing the valves and coils for activating the valves are housed in one unit. An electronic control unit is located in a separate unit and connected to the hydraulic control unit by electrical cable.
Other prior art systems have been designed in which the hydraulic control unit and the electronic control unit are housed as part of the same assembly. In these single assembly configurations, the hydraulic control unit or subassembly must be isolated from the electronic control unit or subassembly. The two subassemblies must be hydraulically isolated. These single assembly prior art devices have solenoid coils located in a coil chamber located between the unit containing the hydraulic valves and the electronic control unit which applies a current to the appropriate coil to activate the corresponding valve. These coils have a winding mounted on a bobbin which is in turn encased in a metallic coil housing. Coil leads extend from the lower coil housing. A number of these individual coils are mounted in a coil chamber housing consisting of a plastic housing having pillars extending upward from the lower surface of the coil housing to define individual, substantially cylindrical, cavities into which individual coils are inserted. A gasket is positioned between the individual coil housing and the floor of the coil chamber housing to provide a resilient spring force between the coil and the floor.
After the coils are inserted in the coil chamber housing, the coil leads extend through openings in the floor of the coil chamber housing where they can be connected to the electronic control unit. This connection can be established by soldering the coil leads to a lead frame molded in the housing. Alternatively they can be soldered directly to a printed circuit board which comprises the main substrate for the electronic control subassembly, or they can be soldered to a separate printed circuit board which is heat staked on the exterior of the floor of the coil chamber housing.
Several different versions of these assemblies, each containing a different number of coils, are commonly used. The same coil chamber housing is typically used for multiple configurations to eliminate the cost of multiple molds. In order to maintain the integrity of the floor of the coil chamber housing, which serves as a sealing bulkhead, these holes must be filled by a separate manufacturing operation, adding additional cost to the product. One method of filling these holes is to pot the lower portion of the inner chamber of the coil chamber housing.
After assembling the coils in the coil chamber housing, this subassembly can be tested for electrical continuity and integrity or this test can be done after interconnection of the coil to the electronic control unit. In either case, any defect in the coils or the coil subassembly will be difficult or impossible to repair, thus adding cost to the final product.